1. Field of the Invention
The present invention relates to a fuel injection valve used in a fuel injection apparatus for injecting fuel into a diesel engine.
2. Description of the Prior Art
In a fuel injection apparatus of a diesel engine, there are required a high injection pressure, a variable injection timing, and a variable fuel injection rate for providing measures to counter engine exhaust gas or particulates pollution, and in a fuel injection valve, it is required to decrease a sack volume, which is a volume between an injection valve seat and a nozzle hole opening to an engine combustion chamber measured in a closed valve condition. For an example, a suckless nozzle 1 shown in FIG. 13 has been proposed.
The suckless nozzle 1 is composed of a valve body 2 having a concave conical surface 22, a recess 23, and fuel injection holes 24, 25 at the inside of the tip of the valve body, and of a needle valve 3 having a cylindrical shaft portion 31, a first conical surface 32 and a second conical surface 33.
In this arrangement, however, when the lift of the needle valve is small, there appears only a narrow gap between the valve body 2 and the needle valve 3. In consequence, the most portion of the pressurized fuel flows through this narrow gap with a high speed towards the recess 23 which is provided for the convenience of fabrication, but not into the fuel injection holes 24, 25, and only a small portion of the fuel flowing into the fuel injection holes flows mainly towards the lower side of the fuel injection holes thereby making the contraction coefficient of the fuel flow very small. As a result, the atomized fuel flows asymmetrically through the outlet regions of the fuel injection holes 24, 25, and the fuel injection angle increases, thereby causing an insufficient fuel flow reach and a deteriorated combustion in the engine.
Further, for solving the problem relating to a sackless nozzle, there is a proposal (SAE 860416) that an annular needle sack is to be formed at the tip of the needle valve. This arrangement, however, has a problem that the fuel flow feature may be rapidly changed, and an inconvenient change of the relation between a needle valve lift amount and a fuel flow sectional area is caused, thereby making it difficult to apply this arrangement to a nozzle having a great lift.